The biological significance of a new microbial vitamin-coenzyme relationship, coenzyme M, will be determined. So far, three biologically active forms of the cofactor have been found in Methanobacterium. Two of these, 2-mercaptoethanesulfonic acid (HSCoM), and 2,2' dithiodiethanesulfonic acid (SSCoM) have vitamin growth-factor properties for certain bacteria. The methylated cofactor, 2- methylthioethanesulfonic acid (CH3SCoM), is a coenzyme methyl-donor for the formation of methane. Experiments will be carried out to define the microbial chemistry of the synthesis of CoM and the origin of the SH, ethane, and sulfonic acid moities. The relationship of CoM analogues such as taurine (found in bile, brain, liver, urine) and isethionic acid (nerve tissue, urine) will be studied. CoM auxotrophs for use in microbial assays will be isolated by chemical and UV mutagenesis by use of a new technique for growing methane bacteria on plates in an anaerobic hood. The distribution of CoM in animal, plant, and microbial tissues will be assayed and its biochemical role there will be defined. The effect of CoM derivatives on the growth of fastidious and difficult to grow microbes (spirochaetes, treponems as well as fastidious nonspore-forming anaerobes from the human gut) will be determined.